Middle T mediated cellular transformation has been a valuable model for studying proteins that regulate cell growth and differentiation. Genetic and biochemical analysis has shown that middle T associates with regulatory molecules such as Src kinases, Shc and PI3'kinase. An examination of the middle T Sequence shows that a region around amino acid 340 is proline rich and is similar to a consensus SH3 binding site. SH3 domains have been found in cytoskeletal proteins as well as signaling molecules making it likely that middle T is interacting with other cellular proteins through this region. The aim of this project is to detect proteins that interact with this putative SH3 binding site. This interaction will be detected using the yeast two hybrid system and coimmunoprecipitation experiments. Isolating target proteins specific for middle T will provide further understanding of the mechanism by which it achieves cellular transformation. This information will be generally valuable for understanding cellular transformation and tumor development.